The present invention generally relates to gas generators such as used to inflate air bags in an automobile occupant protection system, and more particularly to an improved gas generator having a dual chamber inflator body wherein each chamber operates independently of the other.
The prior art generally discloses inflation systems for deploying an air bag in a motor vehicle which provide a single gas generator in fluid communication with the uninflated air bag. The gas generator is typically triggered by an air bag firing circuit when the sensed vehicle acceleration exceeds a predetermined threshold value, as through the use of an acceleration-responsive inertial switch and an explosive "squib."
Conventional single gas generator inflation systems suffer from the disadvantage that the onset pressurization/inflation rate is generally set to provide an aggressive or rapid initial inflation in order to achieve a particular inflation time even for an occupant positioned relatively close to the air bag. However, an aggressive and uncontrolled onset rate of pressurization becomes problematic in situations where the occupant is out of position. More specifically, the rapid pressurization can cause the air bag to impact against the occupant with enough force to injure the occupant.
Occasionally, when single gas generator inflation systems are deployed, smaller occupants, usually children and smaller women, have been seriously injured. The airbag volume and inflating capacity are designed to protect both large and small occupants and are generally not variable within the single gas generator. Therefore, the inflation rate and volume of the airbag may result in an impact potentially hazardous to smaller occupants.
In commonly owned U.S. Pat. No. 5,400,487, Gioutsos et al teach an inflation system which overcomes the above-described problems by utilizing a plurality of gas generators which are controllably ignited to provide a variable inflation profile which can be tailored to any given occupant weight and/or position and for any crash type. While this arrangement dramatically improves the inflation efficiency so as to maximize an air bag's ability to protect an occupant, it does so at significantly higher expense and complexity. More specifically, the multiple gas generators and squibs add considerable cost to the system, while the firing control circuitry requires sophisticated processors capable of accurately timing the various ignition times.
Other designs include nonazide multi- or dual chamber systems that selectively deploy depending on design criteria such as the positioning and/or weight of the occupant, or on the speed of the collision. Dual chamber systems such as these are generally manufactured by welding the integral end closures of two inflator housings together, whereby two chambers are formed with a separating wall therebetween. Each housing is of a predetermined size that is determinative of the nonazide propellant capacity and consequently, of the inflating capability of each chamber. Upon collision, depending on the weight of the passenger, either chamber or both may be selectively ignited thereby inflating the protective airbag.
However, the inherently high ignition temperature of a nonazide propellant charge located in the first chamber produces enough heat energy to heat the separating wall and conductively ignite the nonazide propellant charge located in the second chamber. Therefore, one disadvantage of conventional dual chamber inflators is the likelihood of inadvertent ignition of an adjoining secondary chamber once a selected first chamber has been ignited. When attempting to leave the vehicle after a collision, occupants in positions skewed to the normal riding position may expose themselves to potential injury should an inflator inadvertently ignite and redeploy the airbag. Furthermore, rescuers attempting to remove the occupants from their vehicle may assume positions that could prove harmful should an airbag redeploy unexpectedly.
Finally, laser welding of the dual chamber generators described above is expensive. Furthermore, there is minimal tailorability of the size of the chamber; accordingly, each chamber/propellant tube must be cut and sized prior to welding, thereby accommodating a desired amount of propellant grains. Quite simply, the requirement of sizing the propellant tubes to form different size propellant chambers complicates the manufacturing process.
Therefore, a need still exists for a gas generator which can satisfactorily produce variable inflation pressurization at a reasonable manufacturing cost, and yet prevent hazardous redeployment of the system airbag.